Home-Field Advantage in the NFL

I ended my previous post with a reference to the NFL Road 'Dog System which has continued to be profitable for far longer than might be expected. Just two of the last 17 seasons have been losing ones, and since the league reorganised in 2002, the ROI is 6.6% from 1305 selections with a win percentage of 54.74%.

The basic premise for the system is that bettors continue to consider home-field advantage to be more valuable than it actually is. A covers.com article earlier this year stated that:

For a long time, if you asked any regular NFL bettor what home-field advantage was worth, you more or less got the same answer: three points on the spread. But the collective understanding of what the home field is worth today has evolved rapidly due to a long-standing downward trend, as well as adjustments suggested and made during the nearly fanless season of the COVID pandemic.

Readers of this blog will be familiar with legendary bettor Billy Walters, aka Rick Matthews, and he has an autobiography scheduled to be published later this month titled "Gambler: Secrets from a Life at Risk" which should be an interesting read for many of us. One of the excerpts released early is on this very topic, and this is what Walters has to say:

The standard NFL home-field advantage, taking fanfare, folklore, and conventional wisdom into consideration, is generally thought to be worth 3 points. Well, not so fast. The actual average home-field advantage, taking into account every NFL game from 1974 to 2022, is closer to 2.5 points. In addition, the home-field advantage over the last four years of NFL football is actually less than 1 point (thanks largely to COVID).

If you had made the mistake of using 3 points for the average home-field advantage over the last three years, you certainly would have lost. This is a variable that needs constant updating to keep up with trends. I do a lot of reading and examining scoring trends over time to determine exactly what advantage home field affords.

Walters also mentions some other factors which readers will be familiar with - the impact of Divisional games for example, which again regular readers will already be aware of, and time zones which again have been covered here as an area of opportunity. 

He also points out that you will need to win more than 50% of your (spread) bets to be profitable:

You may think betting is a 50/50 proposition. It is not. Because you must pay a fee to make a bet - usually $11 for every $10 bet - you need to win 52.38 percent of the time to break even.

This is the percentage when you are betting into a -110 book. Pinnacle's -105 lowers the required win percentage to 51.23%, and for Betfair users in a 2% commission market, the number required drops to about 50.76%. 

I love these stories about gamblers such as Billy Walters who are able to consistently beat the odds betting on sports with systems based on mathematics. There are lessons to be learned for all of us, and while none of us is likely to achieve same level of success as the likes of Walters, Alan Woods and Haralabos Voulgaris, with a disciplined approach, it is possible to be profitable. 

In my Numbers, Not Teams post from March 2019, in regard to the challenge of finding winners at a rate above 51.23%, I wrote: 

Given that my grandmother would be expected to pick winners at a rate of around 50%, and she's been dead for over 30 years, this didn't seem to be a hugely impossible task.

My opinion about this remains unchanged.